It very likely means that this ep was numbered with a wrong/different episode number in the EPG.
After the recording is finished, Plex throws away the description from the EPG and downloads metadata from TheTVDB instead.
The only way to keep Plex using the EPG data is to set the default metadata agent to Personal Media.
But careful: This can mess up the metadata of many of the recordings you already have in that library. So I’d try it with a separate library first.
